Observable.Using does not propagate exceptions from resource .Dispose method to stream

#### Bug

System.Reactive 5.0.0, Windows .NET 5.0

There are two error-handling cases with `Observable.Using`:

1. Exception is thrown when **creating** the resource (i.e. in provided resource factory method). In this case, exception is propagated to the resulting stream and can be handled in reactive way by using methods like `.Catch`. **Works as expected**.
2. Exception is thrown when calling `Dispose` method of the resource. If this one throws, exception will be **unhandled, crashing the application regardless of onError handlers**.

Reproduction snippet:
```
static async Task Main(string[] args)
{
var source = Observable.Interval(TimeSpan.FromMilliseconds(50));
var withResource = Observable.Using(
() => Disposable.Create(() =>
{
Console.WriteLine("Disposing");
throw new InvalidOperationException("HA");
}),
_ => source.Take(10));

withResource.Subscribe(Console.WriteLine, ex => Console.WriteLine("Caught error"));
await Task.Delay(10000);

Console.WriteLine("Exiting application");
}
```

Expected `onError` handler to work here but exception is thrown as unhandled, crashing the application.

Is this intended behavior? Seems a bit inconsistent given that clearly measures were taken to ensure proper exception handling in resource creation (see `System.Reactive.Linq.ObservableImpl.Run` method).

I understand that allowing Dispose method to throw is bad design and will of course fix problem in my code, but still, accidents happen.